Measuring functional connectivity in default mode network using Hilbert Envelope Correlation
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1
University of Nottingham, United Kingdom
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2
University of California, Biomagnetic Imaging Laboratory, United States
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3
UCL, United Kingdom
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4
University of California, United States
In recent years, the study of functional connectivity (fc) between brain regions has gained interest. A number of techniques have been developed (e.g. 1) and these have mainly been based on examining the phase relationship between MEG signals either in channel or source space. In this study we introduce a new technique for fc measurement based on Hilbert envelope correlation. Five subjects took part in the experiment. Data were collected using the third order gradiometer configuration of a 275-channel CTF MEG system. Co-registration of MEG data to anatomy was achieved using head digitisation. Data were frequency filtered into alpha, beta and gamma bands. A beamformer was employed to project data into source space. Based on anatomical knowledge, seed locations in posterior cingulate cortex (PCC) were selected; the Hilbert envelope of the timecourse from the seed location and all other brain locations was computed and an image of correlation between envelopes constructed. Source space connectivity measurement is confounded by inverse modelling error and magnetic field spread. A novel correction factor, based on beamformer weights correlation, was therefore developed along with statistical tests to study the significance of results. With a seed in PCC (MNI (0+/-3, -52+/-5, 30+/-6) mm) significant correlation was observed in anterior cingulate cortex (MNI (1+/-9, 20+/-5, -6+/-5)mm) in both the alpha and beta bands in four out of five subjects (average correlation 0.3+/-0.1). In addition, significant correlation was observed in three out of five subjects in the lateral parietal areas. Hilbert envelope correlation can be employed to successfully measure source space fc between nodes of the default mode network, which has previously been described in fMRI. The Hilbert envelope correlation technique complements other fc measurements based on fixed phase relationships.
References
1. Gross et al., PNAS, 98, 694-699, 2003
Conference:
Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010.
Presentation Type:
Poster Presentation
Topic:
Signal proccessing
Citation:
Brookes
M,
Hale
J,
Zumer
J,
Stevenson
C,
Francis
S,
Owen
J,
Barnes
G,
Nagarajan
S and
Morris
P
(2010). Measuring functional connectivity in default mode network using Hilbert Envelope Correlation.
Front. Neurosci.
Conference Abstract:
Biomag 2010 - 17th International Conference on Biomagnetism .
doi: 10.3389/conf.fnins.2010.06.00113
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Received:
23 Mar 2010;
Published Online:
23 Mar 2010.
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Correspondence:
Matthew Brookes, University of Nottingham, Nottingham, United Kingdom, matthew.brookes@nottingham.ac.uk